#include <bits/stdc++.h>

#include <atcoder/all>
#define LL long long
using namespace std;
using namespace atcoder;

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int N;

  cin >> N;
  cout << N * (N + 1) / 2 << "\n";
  return 0;
}
